Controlled fluid transport in microfabricated polymeric substrates

ABSTRACT

Microfluidic devices are provided for the performance of chemical and biochemical analyses, syntheses and detection. The devices of the invention combine precise fluidic control systems with microfabricated polymeric substrates to provide accurate, low cost miniaturized analytical devices that have broad applications in the fields of chemistry, biochemistry, biotechnology, molecular biology and numerous other fields.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S.application Ser. No. 09/179,242 filed Oct. 26, 1998 U.S. Pat. No.6,156,181 which is a continuation of Ser. No. 08/843,212 filed Apr. 14,1997, U.S. Pat. No. 5,885,470 the disclosures of which are incorporatedby reference for all purposes.

This application also claims benefit of provisional Patent ApplicationNo. 60/015,498, filed Apr. 16, 1996, which is hereby incorporated hereinby reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

There has recently been an increasing interest in the application ofmanufacturing techniques common to the electronics industry, such asphotolithography, wet chemical etching, etc., to the microfabrication offluidic devices for use in obtaining chemical and biochemicalinformation.

The manufacture of fluidic devices in solid substrates, e.g., silicon,glass, etc., was described as early as 1979, with the disclosure of theStanford Gas Chromatograph (discussed in Manz et al., Avd. in Chromatog.(1993) 33:1-66, citing Terry et al., IEEE Trans. Electron. Devices(1979) ED-26:1880). These fabrication technologies have since beenapplied to the production of more complex devices for a wider variety ofapplications.

To date, the most prominent use of this technology has been in the areaof capillary electrophoresis (CE). Capillary electrophoresis typicallyinvolves the injection of a macromolecule containing sample, e.g.,nucleic acids or proteins, into one end of a thin capillary. A potentialis then applied along the length of the capillary to electrophoreticallydraw the materials contained within the sample through the channel. Themacromolecules present in the sample then separate from each other basedupon differences in their electrophoretic mobility within the capillary.Such differences in electrophoretic mobility typically result fromdifferences in the charge and/or size of a compound. Other factors canalso affect the electrophoretic mobility of a given compound, such asinteractions between the compound and the capillary walls, interactionswith other compounds, conformation of the compound, and the like.

Capillary electrophoresis methods have traditionally employed fusedsilica capillaries for the performance of these electrophoreticseparations. In more recent applications, this fused silica capillaryhas been replaced by an etched channel in a solid planar substrate,e.g., a glass or silica slide or substrate. A covering layer orsubstrate provides the last wall of the capillary.

Early discussions of the use of this planar substrate technology forfabrication of such devices are provided in Manz et al., Trends in Anal.Chem. (1990) 10(5):144-149 and Manz et al., Adv. in Chromatog. (1993)33:1-66, which describe the fabrication of fluidic devices andparticularly capillary electrophoresis devices, in silicon and glasssubstrates.

Although generally concerned with the movement of material in smallscale channels, as the name implies, capillary electrophoresis methodsemploy electrophoresis to affect that material movement, e.g., themovement of charged species when subjected to an electric field. Whileproviding significant improvements in the separation of materials, thesecapillary electrophoresis methods cannot be used n the direction of bulkmaterials or fluids within microscale systems. In particular, becauseelectrophoresis is the force which drives the movement of materials inCE systems, species within the material to be moved which have differentelectrophoretic mobilities will move at different rates. This results ina separation of the constituent elements of the material. While thistypically is not a problem in CE applications, where separation is theultimate goal, where the goal is the bulk transport of fluid bornematerials from one location to another, electrophoretic separation ofthe constituent elements of that material can create numerous problems.Such problems include excessive dilution of materials in order to ensurecomplete transport of all materials, biasing of a transported materialin favor if faster electrophoresing species and against slower or evenoppositely electrophoresing species.

While mechanical fluid direction systems have been discussed for movingand directing fluids within microscale devices, e.g., utilizing externalpressures or internal microfabricated pumps and valves, these methodsgenerally require the use of costly microfabrication methods, and/orbulky and expensive equipment external to the microfluidic systems.Accordingly, it would generally be desirable to produce a microscalefluidic device that can be easily and cheaply manufactured. The presentinvention meets these and other needs.

SUMMARY OF THE INVENTION

It is a general object of the invention to provide microfluidic devicesfor the performance of chemical and biochemical analyses, syntheses anddetection. The devices of the invention combine precise fluidic controlsystems with microfabricated polymeric substrates to provide accurate,low cost, miniaturized analytical devices that have broad applicationsin the fields of chemistry, biochemistry, biotechnology, molecularbiology and numerous other fields.

In a first aspect, the present invention provides a microfluidic systemwhich includes a microfluidic device. The device comprises a body thatis substantially fabricated from a polymeric material. The body includesat least two intersecting channels disposed therein, where the interiorsurfaces of these channels have a surface potential associatedtherewith, which is capable of supporting sufficient electroosmoticmobility of a fluid disposed within the channels. At least one of thetwo intersecting channels has at least one cross sectional dimension inthe range of from about 0.1 μm to about 500 μm. The device also includesat least first, second and third ports disposed at termini of the firstchannel and at least one terminus of the second channel, and these portsare in electrical contact with fluid in the channels. The system alsoincludes an electrical control system for concomitantly applying avoltage at the three ports, to selectively direct flow of a fluid withinthe intersecting channels by electroosmotic flow.

The present invention also provides a method of fabricating microfluidicdevices for use with an electroosmotic fluid direction system. Themethod comprises molding a polymeric material to form a substrate thathas at least one surface, and at least first and second intersectingchannels disposed in that surface. Each of the at least first and secondIntersecting channels has an interior surface which has a surfacepotential associated therewith, which is capable of supportingsufficient electroosmotic flow of a fluid in those channels. Again, atleast one of the intersecting channels has at least one cross-sectionaldimension in the range of from about 0.1 μm to about 500 μm. A coverlayer is overlaid on the surface of the substrate, whereby the coverlayer encloses the intersecting channels. Together, the substrate andcover layer will also comprise at least three ports disposed therein,each of the at least three ports being in fluid communication with firstand second termini of said first channel and at least one terminus ofthe second channel.

In a related aspect, the present invention also provides a method fordirecting movement of a fluid within a microfluidic device. The methodcomprises providing a microfluidic device having at least first andsecond intersecting channels disposed therein. Each of the first andsecond intersecting channels has a fluid disposed therein, wherein theat least first and second channels have interior surfaces having asurface potential associated therewith, which is capable of supportingsufficient electroosmotic mobility of the fluid disposed In thosechannels. The device also includes at least first, second, third andfourth ports disposed in the substrate, wherein the first and secondports are in fluid communication with the first channel on differentsides of the intersection of the first channel with the second channel,and the third and fourth ports are in fluid communication with thesecond channel on different sides of the intersection of the secondchannel with the first channel. A voltage gradient is then appliedbetween at least two of the first, second, third and fourth ports toaffect movement of said fluid in at least one of the first and secondintersecting channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic illustration of one embodiment of amicrofluidic system.

FIG. 2 is a schematic illustration of one embodiment of a microfluidicdevice of the present invention.

FIG. 3 is a plot illustrating electroosmotic transport of a neutralfluorescent dye past a detector in a microfluidic channel, fabricated ina polymeric substrate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally provides microfluidic devices andsystems, as well as methods for using such devices and systems. Thedevices and systems of the present invention are generally characterizedin that they typically include precise fluid direction and controlsystems, and that they are largely fabricated from polymeric materials.These two characteristics provide the microfluidic devices and systemsof the present invention with a number of advantages over previouslyused materials, such as silica based substrates, semiconductorsubstrates, e.g., silicon, and the like, including ease ofmanufacturing, low cost of materials, and inertness to a wide range ofpotential reaction conditions, including salts, pH and application ofelectric fields. In addition, these devices and systems also aregenerally characterized by their inclusion of, or adaptability toprecise fluid direction and control elements.

I. Microfluidics, Generally

As noted above, the present invention generally relates to microfluidicdevices and systems, which include precise fluid control elements, e.g.,fluid transport and direction systems, and which are fabricated frompolymeric substrates.

The term “microfluidic device” as used herein, refers to a device oraggregation of devices, which includes a plurality of interconnectedchannels or chambers, through which materials, and particularly fluidborne materials may be transported to effect one or more preparative oranalytical manipulations on those materials. Typically, such channels orchambers will include at least one cross sectional dimension that is inthe range of from about 0.1 μm to about 500 μm, and preferably fromabout 1 μm to about 100 μm. Dimensions may also range from about 5 μm toabout 100 μm. Use of dimensions of this order allows the incorporationof a greater number of channels, chambers or sample wells in a smallerarea, and utilizes smaller volumes of reagents, samples and other fluidsfor performing the preparative or analytical manipulation of the samplethat is desired.

The microfluidic device may exist alone or may be a part of amicrofluidic system which can include: sampling systems for introducingfluids, e.g., samples, reagents, buffers and the like, into the device;detection systems; data storage systems; and control systems, forcontrolling fluid transport and direction within the device, monitoringand controlling environmental conditions to which the fluids in thedevice are subjected, e.g., temperature, current and the like. Aschematic illustration of one embodiment of such a system is shown inFIG. 1. As shown, the system includes a microfluidic device 100. Thedevice, and particularly the reagent wells or ports of the device areelectrically connected to voltage controller 110, which controls fluidtransport within the device. An example of a particularly preferredvoltage controller is described in, e.g., U.S. patent application Ser.No. 08/691,632, filed Aug. 2, 1996, and incorpoated herein by referencein its entirety for all purposes. Detection of the output of the deviceis carried out by detector 120. Both detector 120 and voltage controller110 are connected to computer 130, which instructs voltage controller inthe selective application of varying voltage levels to the various portsof the device 100. The computer also receives and stores detection datafrom detector 120, and is typically appropriately programmed to performanalysis of those data.

Microfabricated fluidic substrates have been described for theperformance of a number of analytical reactions. For example, U.S. Pat.No. 5,498,392 to Wilding is and Kricka, describes a mesoscale apparatuswhich includes microfabricated fluid channels and chambers in a solidsubstrate for the performance of nucleic acid amplification reactions.Further, U.S. Pat. No. 5,304,487 to Wilding and Kricka also describes amesoscale device for detecting an analyte in a sample which deviceincludes a cell handling region. The device also includesmicrofabricated channels and chambers having at least onecross-sectional dimension in the range of from 0.1 μm to about 500 μm.Similar devices are also described in U.S. Pat. Nos. 5,296,375,5,304,487, 5,427,946, and 5,486,335, also to Wilding and Kricka, fordetection of cell motility and fluid characteristics, e.g., flowrestriction as a function of analyte concentration. The disclosure ofeach of these patents is incorporated herein by reference.

III. Polymeric Substrates

Typically, fabrication of fluidic systems having small or evenmicroscale dimensions has drawn on techniques that are widely used inthe electronics industry, such as photolithography, wet chemicaletching, controlled vapor deposition, laser drilling, and the like. As aresult, these microfabricated systems have typically been manufacturedfrom materials that are compatible with these manufacturing techniques,such as silica, silicon, gallium arsenide and the like. While each ofthese materials is well suited for microfabrication, and many are wellsuited for inclusion in microfluidic systems, the costs associated withthe materials and manufacture of devices utilizing such materialsrenders that use commercially impractical.

The present invention on the other hand, is characterized in that thedevices are substantially fabricated from polymeric materials. By“Polymeric Substrates” or “Polymeric Materials” is generally meantorganic, e.g., hydrocarbon based, polymers that are capable of formingrigid or semi-rigid structures or substrates. By “substantiallyfabricated from polymeric materials” is meant that greater than 50%(w/w) of the materials used to manufacture the microfluidic devicesdescribed herein are polymeric materials. For example, while a substratemay be fabricated entirely of a polymeric material, that substrate mayalso include other non-polymeric elements incorporated therein,including, e.g., electrodes, glass or quartz detect on windows, glasscover layers and the like. Typically, the devices of the presentinvention comprise greater than 60% polymeric materials, preferablygreater than 70%, more preferably greater than 80% and often greaterthan 95% polymeric materials.

Microfabrication of polymeric substrates for use in the devices of theinvention may be carried out by a variety of well known methods. Inparticular, polymeric substrates may be prepared using manufacturingmethods that are common in the microfabrication industry, such asinjection molding or stamp molding/embossing methods where a polymericsubstrate is pressed against an appropriate mold to emboss the surfaceof the substrate with the appropriate channel structures. Utilizingthese methods, large numbers of substrates may be produced using, e.g.,rolling presses or stamps, to produce large sheets of substrates.Typically, these methods utilize molds or stamps that are themselves,fabricated using the above-described, or related microfabricationtechniques.

Although generally not preferred for the manufacture of polymericsubstrates for cost reasons, other microfabrication techniques are alsosuitable for preparation of polymeric substrates, including, e.g., laserdrilling, etching techniques, and photolithographic techniques. Suchphotolithographic methods generally involve exposing the polymericsubstrate through an appropriate photolithographic mask, i.e.,representing the desired pattern of channels and chambers, to adegradative level of radiation, e.g., UV light for set periods of time.The exposure then results in degradation of portions of the surface ofthe substrate resulting in the formation of indentations whichcorrespond to the channels and/or chambers of the device.

Suitable polymeric materials for use in fabricating substrates aregenerally selected based upon their compatibility with the conditionspresent in the particular operation to be performed by the device. Suchconditions can include extremes of pH, temperature and saltconcentration. Additionally, substrate materials are also selected fortheir inertness to critical components of an analysis or synthesis to becarried out by the device, e.g., proteins, nucleic acids and the like.

Polymeric substrate materials may be rigid, semi-rigid, or non-rigid,opaque, semi-opaque or transparent, depending upon the use for whichthey are intended. For example, devices which include an optical orvisual detection element, e.g., for use in fluorescence based orcalorimetric assays, will generally be fabricated, at least in part,from a transparent polymeric material to facilitate that detection.Alternatively, transparent windows of, e.g., glass or quartz, may beincorporated into the device to allow for these detection elements.Additionally, the polymeric materials may have linear or branchedbackbones, and may be cross-linked or non-cross-linked. Examples ofpreferred polymeric materials include, e.g., polydimethylsiloxanes(PDMS), polymethylmethacrylate (PMMA), polyurethane, polyvinylchloride(PVC), polystyrene, polysulfone, polycarbonate and the like.

Typically, the polymeric substrates used in the devices of the presentinvention are fabricated in two or more parts. Specifically, a firstplanar substrate element is provided having a plurality of groovesand/or wells, corresponding to the fluid channels and/or chambers,manufactured, e.g., molded or machined, into one of its planar surfaces.These grooves provide the bottom and side walls of the channels andchambers of the devices. A second planar substrate element is then matedwith the first to define the top wall of the channels and chambers. Thetwo members are bonded together in order to ensure that the channels andchambers in the substrate are fluid tight. Bonding of the two membersmay be accomplished by a number of methods that are known in the art,such as through the use of adhesives, e.g., UV curable adhesives, or bysonically welding one member to the other, e.g., as described inPublished PCT Application No. WO 95/12608, which is incorporated hereinby reference in its entirety for all purposes. Alternatively, the twoplanar elements may be bonded by applying pressure to the joined pairunder elevated temperatures, sufficient to bond the two planar elementstogether.

As described above, the polymeric substrate may be rigid, semi-rigid,nonrigid or a combination of rigid and nonrigid elements, depending uponthe particular application for which the device is to be used. In oneparticular embodiment, a substrate is made up of at least one softer,flexible substrate element and at least one harder, more rigid substrateelement, one of which includes the channels and chambers manufacturedinto its surface. Upon mating the two substrates, the natural adhesionof the soft, less rigid substrate, either to another less rigidsubstrate or to a more rigid substrate, allows formation of an effectivefluid seal for the channels and chambers, obviating the difficultiesassociated with gluing or melting more rigid plastic componentstogether.

III. Fluid Direction System

The devices of the present invention, in addition to being largelyfabricated from polymeric substrates, also are generally characterizedby the use of fluid transport and direction systems that do not employmechanical pumps or valves, or the application of external pressure toselectively move and direct the fluids through the various channels orchambers contained in the device or system. Instead, the microfluidicdevices and systems of the present invention typically utilizecontrolled electroosmotic flow to transport and selectively directfluids among and through the interconnected series of channels containedwithin the device. One example of such controlled electroosmotic flow isdescribed in published International Patent Application No. WO 96/04547to Ramsey, which is incorporated herein by reference in its entirety forall purposes.

In brief, when an appropriate fluid is placed in a channel or otherfluid conduit having functional groups present at the surface, thosegroups can ionize. For example, where the surface of the channelincludes hydroxyl functional groups at the surface, i.e., as in the caseof silica, protons can leave the surface of the channel and enter thefluid. Under such conditions, the surface will possess a net negativecharge, whereas the fluid will possess an excess of protons or positivecharge particularly localized near the interface between the channelsurface and the fluid. By applying an electric field across the lengthof the channel, cations will flow toward the negative electrode.Movement of the positively charged species in the fluid pulls thesolvent with them. The steady state velocity of this fluid movement inthe channel is directly proportional to the zeta potential of thesurface that is in contact with the fluid being moved (See, e.g.,Published International Application No. WO. 96/04547, previouslyincorporated herein).

Fluid velocity within a channel is also generally given as:

v=(μEO)E

Where v is the velocity of the fluid, μEO is the electroosmotic mobilityof the fluid in the system, and E is the electric field strength. Thus,the electroosmotic mobility of the fluid is also directly proportionalto the zeta potential of the surface that is contacting the fluid.

The fluid flow rate, or volume velocity, within a specific channel (Q)is then given as:

Q=(μEO)EA

where μEO and E are as defined above, Q is the volume velocity of thefluid and A is the cross sectional area of the channel through which thefluid is flowing. Using the above equations, therefore, one cancalculate the electroosmotic mobility of a given fluid in a givenchannel from either its velocity or its volumetric flow rate, e.g., incm³/second.

Accordingly, the electroosmotic fluid control systems employed in thedevices of the present invention generally require channels havingsurfaces with sufficient zeta potentials to propagate an acceptablelevel of electroosmotic mobility within those channels.

This zeta potential requirement, in combination with the availability ofsuitable manufacturing techniques as described above, has resulted insilica substrates generally being employed for systems utilizing suchelectroosmotic flow. Optimized planar silica substrates having channelsfabricated into their surfaces, have generally supported anelectroosmotic mobility of approximately 5×10⁻⁴ cm²V⁻¹s⁻¹ for a 5 mMSodium borate buffer at pH 7, that is disposed within those channels.

However, as noted above, the devices and systems of the presentinvention utilize polymeric substrates. In general, such polymericmaterials generally have hydrophobic surfaces and will have relativelylow surface potentials, generally making them less suitable forelectroosmotic flow systems.

Accordingly, incorporation of the electroosmotic fluid control systemsdescribed above, into the polymeric substrates used in the presentinvention, typically requires either: (1) selection of a polymericmaterial which has a surface potential capable of supporting sufficientelectroosmotic mobility of a fluid disposed in contact with thatsurface; or (2) modification of the surfaces of the polymeric substratethat are to be in contact with fluids, to provide a surface potentialthat is capable of supporting sufficient electroosmotic mobility. Asused herein, the phrase “support sufficient electroosmotic mobility”means that the surfaces in contact with the fluid, e.g., the walls of achannel, possess a sufficient zeta potential, whereby those surfaces orchannel walls are capable of supporting an electroosmotic mobility (μEO)of at least about 1×10⁻⁵ cm²V⁻¹s⁻¹, for a buffer when that buffer is incontact with those walls, e.g., disposed within those channels, e.g., abuffer of from about 1 mM to about 100 mM sodium borate at a pH of fromabout 6 to about 9. For the purposes of the present invention, μEO isreferred to in terms of a standard buffer of from about 1 mM to about 10mM sodium borate buffer, at a pH of from about 7 to about 9, forexample, 5 mM sodium borate, pH 7. In preferred aspects, the surfaces incontact with the fluid are capable of supporting a μEO under the aboveconditions, of at least about 2×10⁻⁵ cm²V³¹ ¹s⁻¹, preferably, at leastabout 5×10⁻⁵ cm²V⁻¹s⁻¹, and in particularly preferred aspects, at leastabout 1×10⁻⁴ cm²V⁻¹s⁻¹.

Although the above listed polymeric materials possess sufficient surfacepotential to support sufficient electroosmotic mobility of fluids incontact therewith, in the case of many polymeric materials, the surfacepotential is so low that it does not support sufficient electroosmoticmobility, as defined above. As such, systems that employ these polymericmaterials, without modification, are largely commercially impracticalfor use in microfluidic devices, due to the extremely slow ratesattainable for fluid transport.

Accordingly, in particularly preferred aspects, the surfaces of thepolymeric material that are to be in contact with the fluids ofinterest, and thus contributing and supporting E/O mobility, aresubjected to modification to effectively increase the zeta potential ofthose surfaces, and thus improve E/O mobility achievable within devicesfabricated from these materials.

Surface modification of polymeric substrates may take on a variety ofdifferent forms, including coating those surface with an appropriatelycharged material, derivatizing molecules present on the surface to yieldcharged groups on that surface, and/or coupling charged compounds to thesurface.

One example of an embodiment employing a surface coating method involvesusing a polymeric substrate which includes a surface that comprises afluorocarbon polymer, e.g., polytetrafluoroethylene (TEFLON), which onits own has a very low surface potential. The substrate may befabricated in whole or in part from the fluorocarbon polymer, oralternatively, the polymer may be applied as a coating on a polymericsubstrate of a different composition.

The surfaces of the substrate that are to be in contact with the fluidare then treated with charged, fluorinated modifier compounds,commercially available from, e.g., J & W Scientific (Folsom, Calif.).These fluorinated modifier compounds interact with the fluorocarbonpolymer surface of the substrate to present charged functional groups atthat surface. These modifiers are available in anionic or cationicforms.

The coating of the surfaces that are intended to contact the fluidswithin the device may be performed on the assembled microfluidic device,e.g., by pumping the perfluoronated compounds through the channelsand/or chambers of the device. Alternatively, the entire surface of thesubstrate, including the surfaces of the channels and chambers, may besubjected to treatment, e.g., by immersion in or deposition of thesecompounds on that surface.

In a related aspect, detergents with their charged head groups andhydrophobic tails, function as particularly desirable coating materials.Upon passing such materials through the channels of the system, thehydrophobic tails of the detergent will localize to the hydrophobicsurface of the substrate, thereby presenting the charged head group tothe fluid layer, creating a charged surface. More particularly,preparation of a charged surface on the substrate involves the exposureof the surface to be modified, e.g., the channels and/or reactionchambers, to an appropriate solvent which partially dissolves or softensthe surface of the polymeric substrate. Selection of appropriatesolvents will generally depend upon the polymeric material that is usedfor the substrate. For example, chlorinated hydrocarbon solvents, i.e.,trichloroethane (TCE), dichloroethane and the like, are particularlyuseful as solvents for use with PMMA and polycarbonate polymers.

A detergent solution is then contacted with the partially dissolvedsurface, whereby the hydrophobic portion of the detergent molecules willassociate with the partially dissolve polymer. A wide variety ofdetergents may be used in this method, and are generally selected basedupon their compatibility with the ultimate end use of the microfluidicdevice or system, including without limitation, for example, SDS (sodiumdodecyl sulfate), DTAB (dodecyltrimethylammonium bromide), or CTAB(cetyltrimethylammoniumbromide). Following contacting the polymer withthe appropriate detergent, the solvent is then washed from the surface,e.g., using water, whereupon the polymer surface hardens with thedetergent embedded into the surface, presenting the charged head groupto the fluid interface.

Differentially charged areas may be selected and prepared using aphotolyzable detergent, which photolyzes to produce a positively ornegatively charged group. Irradiation of selected areas on the substratesurface then fields these charged groups in these areas.

In alternative aspects, the polymeric materials, either as thesubstrate, or as a coating on the substrate, may themselves be modified,derivatized, etc., to present an appropriate zeta potential at the fluidinterface.

For example, once a polymeric material has been molded or otherwisefabricated into a substrate as described herein, the surfaces of thatsubstrate may be modified or activated, e.g., by oxygen plasmairradiation of those surfaces. Polydimethylsiloxane (PDMS), for example,may be modified by plasma irradiation, which oxidizes the methyl groupspresent in the polymer, liberating the carbon atoms and leaving hydroxylgroups in their place. This modification effectively creates aglass-like surface on the polymeric material, with its associatedhydroxyl functional groups. As noted above, this type of surface is wellsuited for propagation of electroosmotic mobility of fluids.

In an alternate but related aspect, block copolymers may be used incombination with the polymer of interest, to present an appropriatesurface for the device. For example,polytetrafluoroethylene/polyurethane block copolymer may be mixed with apolyurethane polymer prior to molding the substrate. The immiscibilityof the polytetrafluoroethylene portion of the copolymer in thepolyurethane results in that copolymer localizing at the surface of thepolyurethane substrate. This surface can then be treated as describedabove, e.g., using fluorinated buffer modifiers.

IV. Microfluidic Devices

As noted above, the devices and systems of the present invention arecharacterized in that they are fabricated largely from polymericsubstrates, and in that they employ controlled electroosmotic flow inselectively transporting and directing fluids through interconnectedchannels and/or chambers, that are contained within these microfluidicsystems. By “selectively transporting and directing” is meant thetransporting of fluids through miroscale or microfluidic channels, andthe selective direction, e.g., dispensing, aliquoting or valving, ofdiscrete quantities of those fluids among interconnected channels, e.g.,from one channel to another.

Accordingly, in preferred aspects, the devices and systems of theinvention generally comprise a body having at least two intersectingchannels disposed within it, which body is fabricated, at least in-part,from a polymeric material. Typically, the body includes a polymericsubstrate having the intersecting chancels fabricated into asubstantially flat surface of the substrate as grooves. A cover is thenoverlaid on this surface to seal the grooves and thereby form thechannels.

In order to effectively and accurately control fluid direction inintersecting channel structures, the fluid direction systems used in thedevices and systems of the present invention typically include aplurality of ports or reservoirs that are in electrical contact andtypically in fluid communication with the channels on different sides ofthe various intersections. Typically, such ports are placed at and inelectrical contact with the free termini of the intersecting channels.By “free terming” or “free terminus” is generally meant that aparticular terminus of a channel is not the result of an intersectionbetween that channel and another channel. Often such ports compriseholes disposed through the cover layer which overlays the firstsubstrate, thereby forming wells or reservoirs at these channel termini.

These ports generally provide an access for electrodes to be placed incontact with fluids contained within the channels, as well as providingan access for introducing fluids, and reservoirs or storing fluids inthe devices.

Although they can exist as part of a separate device employed in anoverall microfluidic system, a number of additional elements may beadded to the polymeric substrate to provide for the electroosmotic fluidcontrol systems. These elements may be added either during the substrateformation process, i.e., during the molding or stamping steps, or theymay be added during a separate, subsequent manufacturing step. Theseelements typically include electrodes for the application of voltages tothe various fluid reservoirs, and in some embodiments, voltage sensorsat the various channel intersections to monitor the voltage applied.

Where electrodes are included as an integrated element of themicrofluidic device, they may be incorporated during the moldingprocess, i.e., by patterning the electrodes within the mold so that uponIntroduction of the polymeric material into the mold, the electrodeswill be appropriately placed and fixed within the substrate.Alternatively, the electrodes and other elements may be added after thesubstrate is formed, using well known microfabrication methods, e.g.,sputtering or controlled vapor deposition methods followed by chemicaletching, and the like.

In operation, the materials stored in the reservoirs are transportedelectroosmotically through the channel system, delivering appropriatevolumes of the various materials to one or more regions on the substratein order to carry out a desired analysis or synthesis.

To provide such controlled electroosmotic flow, the microfluidic systemincludes a voltage controller electrically connected to electrodesplaced or fabricated into the various reagent wells on the device. Thevoltage controller is capable of applying selectable voltage levels, toeach of the ports or reservoirs, including ground. Such a voltagecontroller can be implemented using multiple voltage dividers andmultiple relays to obtain the selectable voltage levels desired.Typically, the voltage controller is interfaced with a computer or otherprocessor, e.g., a PC compatible Pentium microprocessor based orMacintosh Power PC computer, which is programmed to instruct appropriateapplication of voltages to the various electrodes.

In operation, fluid transport within these devices is carried out byapplying a voltage gradient along the path of desired fluid flow,thereby electroosmotically driving fluid flow along that path. Somemethods for affecting electroosmotic fluid flow incorporate a “floatingport” fluid direction system, where a sample fluid in one reservoir andchannel is drawn across the intersection of that channel with anotherchannel, by applying a voltage gradient along the length of the firstchannel, i.e., by concomitantly applying a voltage to the two ports atthe ends of the first channel. Meanwhile, the two ports at the ends ofthe second channel are allowed to “float,” i.e., no voltage is applied.The plug of sample fluid at the intersection is then drawn into thesecond channel by applying a potential to the electrodes at each end ofthe second channel. While this method allows injection of a sample ofone fluid into a different channel, a number of disadvantages remain. Inparticular, leakage can occur at he sample intersection as a result offluid convection, e.g., fluid from one channel “bleeds over” into theother channel. This bleeding over effect can result in imprecise andnonreproducible fluid movements, which can be problematic where onedesires more precise fluid control.

However, in preferred aspects, the fluid control and direction systemsincorporated into the systems of the present invention apply voltages tomultiple reservoirs, simultaneously. In the case of a fluid beingtransported in a first channel through an intersection with a secondchannel, this permits the introduction of constraining or directingflows from the second channel, whereby one can precisely control thelevel of fluid flow in a given direction. This simultaneous applicationof potential to multiple ports allows for specific control of the fluidat the intersection of the channels, reducing or eliminating theconvective effects that are generally seen with floating port methods.For example, a fluid of interest flowing through an intersection of twochannels may be precisely constrained by flowing additional fluids fromthe side channels by appropriate, simultaneous application of voltagesto the reservoirs or ports at the ends of those channels, resulting inthe fluid of interest being maintained in a “pinched” conformation whichprevents bleeding over into the side channels. The volume of the fluidof interest contained within the intersection is readily calculablebased upon the volume of the intersection, and also is readilyreproducible. Further, this volume of fluid can be readily diverted toone of the intersecting channels by appropriate modulation of thepotentials applied at each reservoir or port.

In a related aspect, fluid flow in a first channel past an intersectionwith a second channel may be “gated” or “valved” by fluid flow in thesecond channel through that intersection. Although described in terms ofa valve, it will be readily apparent that fluid direction using thesemethods requires no actual mechanical valve, but instead relies uponapplication of electrical forces through the intersection.

By opening and closing the “valve” through appropriate switching ofvoltage applied to the reservoirs, one can effectively meter the amountof fluid flowing in the first channel past the intersection. Bothpinched and gated control systems are described in significant detail inpublished International Application No. WO 96/04547, previouslyincorporated by reference.

In addition to these pinched and gated flow systems, application thesimultaneous application of voltages at multiple, e.g., three or moreports, permits controlled fluid flow in more complex interconnectedchannel structures. For example, in flowing of fluids throughinterconnected parallel channels, voltages may be applied to multiplereservoirs in order to drive simultaneous flow in the parallel channelswithout the generation of transverse electric fields which caneffectively short circuit the system.

As alluded to above, incorporation of these electroosmotic flow systemsinto the microfluidic devices and systems of the present invention,generally obviates the need for the incorporation of mechanical fluiddirection systems, e.g., microfabricated pumps, valves and the like,within the device itself, or for external fluid movement systems whichrely upon pressure flow of materials, e.g., pneumatic systems.Effectively, such systems provide virtual pumps and valves for fluidtransport and direction, which pumps and valves have no moving parts.

The number of ports at which voltage may be simultaneously controlledwill generally depend upon the complexity of the operation to beperformed by the device. Typically, the devices of the invention willinclude at least three ports at which the voltage is simultaneouslycontrolled, preferably, at least four, more preferably at least five,and in some embodiments will employ six or more ports where the voltageis simultaneously controlled.

FIG. 2 is an illustration of a microfluidic device according to thepresent invention. As shown, the device 100, comprises a body, which isentirely or substantially fabricated from a polymeric material. The bodyincludes a plurality of interconnected channels disposed in it, for thetransport and direction of fluids.

As shown in FIG. 2, the device 100 is fabricated from a planar substrate202, which has the various channels fabricated into its surface. Asecond planar layer overlays the first and includes holes disposedthrough it to form the various reservoirs (cover layer not shown). Thesereservoirs also serve as the ports at which the various electrodes areplaced into electrical contact with fluids in the system. This secondplanar element is then bonded to the first.

The device illustrated, includes a main fluid channel 204 which runslongitudinally down the central portion of the substrate 202. The mainchannel 204 originates in and is in fluid communication with bufferchannel 206, and terminates, and is in fluid communication with wastereservoirs 208. Buffer channel 206 is in fluid communication with twobuffer reservoirs 210 and 212. The device is shown having a number ofchannels intersecting the main channel 204. For example, buffer channel214 terminates in, and is in fluid communication with main channel 204near its originating point, and is at its other terminus, in fluidcommunication with buffer reservoir 216. Sample introduction channel 218also terminates in and is in fluid communication with main channel 204,and is, at its other terminus, in fluid communication with samplereservoir 220. Additional buffer/waste channels 222 and 224, andbuffer/waste reservoirs 226 and 228 are also shown. A detection window230, i.e., for detecting the transit of fluorescent or other dyes isalso shown. The descriptors for the various wells and channels areprimarily offered for purposes of distinguishing the various channelsand wells from each other. It will be appreciated that the various wellsand channels can be used for a variety of different reagents, dependingupon the analysis to be performed.

Application of an electroosmotic flow system into the device showninvolves placing electrodes into electrical contact with each of thevarious reservoirs. By modulating the voltages applied at each of theseelectrodes, e.g., applying voltage gradients across selectedflow/current paths, one can selectively control and direct fluidflow/material transport within the device, as described above. In someaspects, the fluid control system may include optional sensor channels(not shown), for monitoring the voltage at the various intersections.

Although illustrated in terms of a seven reservoir microfluidic device,electroosmotic fluid direction systems can be readily employed in thetransport and direction of materials in more complex channel structuresfor performing a variety of specific manipulations, analyses,preparations, and the like. Examples of such channel structures aredescribed in copending, commonly owned U.S. application Ser. No.08/761,575, filed Dec. 6, 1996, and incorporated herein by reference inits entirety for all purposes.

V. Applications

The microfluidic devices and systems of the present invention arecapable of broad application and may generally be used in theperformance of chemical and biochemical synthesis, analysis anddetection methods. Generally, the devices of the invention can replaceconventional laboratory equipment and methods, including measuring anddispensing equipment, as well as more complex analytical equipment,e.g., HPLC, SDS-PAGE, and immunoassay systems.

For example, these devices may be employed in research, diagnostics,environmental assessment and the like. In particular, these devices,with their micron and submicron scales, volumetric fluid controlsystems, and integratability, may generally be designed to perform avariety of chemical and biochemical operations where these traits aredesirable or even required. In addition, these devices may be used inperforming a large number of specific assays that are routinelyperformed at a much larger scale and at a much greater cost, e.g.,immunoassays.

The devices may also be used to carry out specific operations in theanalysis or synthesis of a sample. For example, the devices may includereaction chambers for performing synthesis, amplification or extensionreactions. The devices may similarly include sample analysis elementsfor the detection of a particular characteristic of the sample, such asa capillary channel for performing electrophoresis on the sample. Insuch cases, and as described previously, devices for use in suchdetection methods will generally include a transparent detection windowfor optical or visual detection.

Examples of some more specific applications of these devices are setforth in, e.g., U.S. patent application Ser. No. 08/761,575, previouslyincorporated herein by reference, and commonly assigned U.S. patentapplication Serial No. 60/086,240, filed Apr. 4, 1997, also incorporatedherein by reference in its entirety.

EXAMPLES Example 1

Fluid Direction in a Polymethylmethacrylate Substrate (PMMA)

Microfluidic devices were fabricated in polymethylmethacrylate (PMMA)using various methods, including: (1) casting a polymer precursoragainst the inverted replica of the channel geometry; and (2) embossinga solid sheet of PMMA against the inverted replica by applying suitabletemperature and pressure.

An inverted replica of a microfluidic device having the channel geometryshown in FIG. 2, was fabricated from silicon using inverted lithography,i.e., etching away the surface everywhere except where the channels wereto be located. This was done with an anisotropic etch (hot KOH) so thatthe sidewalls of the raised channels were planes at an angle of 55°. Theresulting raised channels were 10.87 μm high.

A polymethylmethacrylate polymer was cast against the above-describedsilicon mold, and this casting was bonded to another planar piece ofPMMA which had holes drilled through it to provide the sample andreagent wells. Bonding was carried out by applying pressure andtemperature of 98° C. The resulting device was used for subsequentanalysis.

In order to demonstrate the ability to switch electroosmotic flow in aPMMA device, and to measure the magnitude of that flow, the abovedescribed device was filled with 100 mM borate buffer, at pH 7. Aneutral marker, Rhodamine B, diluted in running buffer, was aliquotedinto reservoir 226 (as referenced in FIG. 2). The neutral marker isfluorescent to allow for its detection, and uncharged, so that it willmove with the flow of buffer, and thus indicate electroosmotic flow ofthe buffer, rather than electrophoretic mobility of the marker.

The running protocol flowed the rhodamine dye from reservoir 226 toreservoir 228, across the intersection of channels 222/224 and channel204 (injection point) prior to injection. Sample flow was detected, notat detection window 230, but instead, at a point in the main channel3.25 mm from the injection point, before the channel turns towardsreservoir 216.

Detection of rhodamine was carried out using a Nikon inverted MicroscopeDiaphot 200, with a Nikon P101 photometer controller, for epifluorescentdetection. An Opti-Quip 1200-1500 50 W tungsten/halogen lamp coupledthrough a 10× microscope objective provided the light source. Excitationand emission wavelengths were selected with a DAPI filter cube (Chroma,Brattleboro Vt.) fitted with an appropriate filter.

In this experiment, the total path length between reservoirs 208 and216, along which the running voltage was applied, was 52 mm. The voltageapplied along this channel was 1200 V, yielding an electric field of 235V/cm. Rhodamine B sample plugs at the injection point were injected at400 second intervals. A plot of fluorescent intensity detected at thedetection point vs. time is shown in FIG. 3.

The time needed for the sample to travel the 3.25 mm from the injectionpoint to the detection point was 85 seconds, translating to a velocityof 3.8×10⁻³ cm/s. It was therefor concluded that the electroosmoticmobility of the buffer under these conditions was 1.6×10⁻⁵ cm²/Vs.

Example 2

Electroosmotic Flow in Injection Molded PMMA Substrate

A similar experiment to that described above, was performed in amicrofluidic device having a single channel connecting two reservoirs orwells. In this experiment, the device was fabricated by injectionmolding the first planar substrate using PMMA (Acrylite M30), whichdefined the channel of the device, and bonding a drilled second planarPMMA substrate to seal the channels and provide the reservoirs. Again,bonding was done with pressure at elevated temperatures, e.g., 85° C.and 2-5 kg pressure.

The channel and reservoirs of the device were filled with 10 mM sodiumborate running buffer, at pH 8.0, and Rhodamine was additionally placedin one reservoir. 2000V were applied to the rhodamine containingreservoir with 1500V applied to the other reservoir. This yielded anapplied voltage of 500V along the channel connecting the two wells.Detection was carried out at a point in the channel, 2.2 cm from therhodamine containing reservoir. Transit time for the dye from itsreservoir to the detection point was 187 seconds and 182 seconds induplicate runs, yielding an average μEO of 5.25×10⁻⁵ cm²V⁻¹s⁻¹.

While the foregoing invention has been described in some detail forpurposes of clarity and understanding, it will be clear to one skilledin the art from a reading of this disclosure that various changes inform and detail can be made without departing from the true scope of theinvention. All publications and patent documents cited in thisapplication are incorporated by reference in their entirety for allpurposes to the same extent as if each individual publication or patentdocument were so individually denoted.

We claim:
 1. A microfluidic device, comprising: a body structurecomprising at least one polymeric material, the body structure having atleast a first microchannel disposed therein, which at least firstmicrochannel comprises at least a first fluidic material, which firstfluidic material is electroosmotically flowed through the at least firstmicrochannel at a mobility of at least about 1×10⁻⁵ cm²V⁻¹s⁻¹.
 2. Themicrofluidic device of claim 1, wherein the first fluidic materialcomprises a sodium borate buffer having an ionic strength between about1 and about 100 mM and a pH from about 6 to about
 9. 3. The microfluidicdevice of claim 2, wherein the first fluidic material has an ionicstrength between about 1 and about 10 mM and a pH from about 7 to about9.
 4. The microfluidic device of claim 1, wherein the at least firstmicrochannel has a zeta potential associated therewith, which zetapotential supports electroosmotic flow of the first fluidic material inthe at least first microchannel.
 5. The microfluidic device of claim 1,further comprising at least a second microchannel intersecting the firstmicrochannel within the polymeric body structure.
 6. The microfluidicdevice of claim 1, further comprising at least one well fluidlyconnected to the first microchannel.
 7. The microfluidic device of claim1, further comprising: at least one well fluidly connected to the firstmicrochannel, wherein an electrode is disposed within the well.
 8. Themicrofluidic device of claim 1, further comprising a well fluidlyconnected to the first microchannel, which well comprises at least aportion of the first fluidic material, the device further comprising avoltage controller in electrical contact with the first fluidic materialin the well or a pressure source fluidly coupled to the well.
 9. Themicrofluidic device of claim 1, further comprising: a well fluidlyconnected to at least the first microchannel; a voltage controller inelectrical contact with a fluid in the well; a computer operably linkedto the voltage controller; and, a detector mounted proximal to the atleast one microchannel for viewing an analyte in the microchannel. 10.The microfluidic device of claim 9, wherein the detector provides datato the computer.
 11. The microfluidic device of claim 1, wherein thebody structure is fabricated by bonding a first polymeric substrate to asecond polymeric substrate, wherein at least the first microchannel isformed between the first polymeric substrate and the second polymericsubstrate.
 12. The microfluidic device of claim 1, wherein saidpolymeric material is selected from: polydimethylsiloxane (PDMS),polyurethane, polyvinylchloride (PVC), polystyrene, polysulfone,polycarbonate, polymethylmethacrylate (PMMA), andpolytetrafluoroethylene.
 13. The microfluidic device of claim 1, thebody structure comprising at least about 50% polymeric materials. 14.The microfluidic device of claim 1, the body structure comprising apolymeric substrate and a cover layer, the polymeric substratecomprising the first microchannel embossed therein, the cover layerdisposed over at least a portion of the first microchannel.
 15. Themicrofluidic device of claim 14, wherein the cover layer is laminated tothe polymeric substrate.
 16. The microfluidic device of claim 14,wherein the cover layer is laminated to the polymeric substrate by oneor more of: adhesive bonding, sonic welding, pressure bonding, thermalbonding, and thermal bonding under pressure.
 17. The microfluidic deviceof claim 14, wherein the cover layer and the polymeric substrate arefused.
 18. The microfluidic device of claim 14, wherein the cover layeris substantially fabricated from glass or a polymer or a combinationthereof.
 19. The microfluidic device of claim 14, wherein the firstmicrochannel is embossed as at least one groove in a substantiallyplanar portion of the polymeric substrate and wherein the cover layeroverlays the at least one groove, thereby forming a closed microchannel.20. The microfluidic device of claim 1, the first fluidic materialhaving an electroosmotic mobility of at least about 5×10⁻⁵ cm²V⁻¹s⁻¹ inthe first microchannel.
 21. The microfluidic device of claim 1, thefirst fluidic material having an electroosmotic mobility of at leastabout 1×10⁻⁴ cm²V⁻¹s⁻¹ in the first microchannel.
 22. The microfluidicdevice of claim 1, wherein the first microchannel comprises a surfacecoating.
 23. The microfluidic device of claim 1, wherein the firstmicrochannel comprises a surface coating, which coating is provided tothe first microchannel by a process selected from: exposure to afluorinated modifier compound, exposure to a detergent, exposure to amaterial having charged functional groups associated therewith, andexposure to a fluorocarbon.
 24. The microfluidic device of claim 1,wherein the at least one microchannel comprises a glass or quartzdetection window.
 25. The microfluidic device of claim 1, the bodystructure comprising at least two intersecting microchannels disposedtherein, each of the at least two intersecting microchannels comprisinga fluid having an electroosmotic mobility of at least about 1×10⁻⁵cm²V⁻¹s⁻¹.
 26. The microfluidic device of claim 25, wherein said fluidcomprises a sodium borate buffer having an ionic strength between about1 and about 100 mM and a pH from about 6 to about
 9. 27. Themicrofluidic device of claim 26, wherein said fluid comprises a sodiumborate buffer having an ionic strength between about 1 and about 10 mMand a pH from about 7 to about
 9. 28. The microfluidic device of claim25, the body structure further comprising at least first, second, thirdand fourth ports in fluid communication with the at least twointersecting microchannels.
 29. The microfluidic device of claim 1,wherein the first microchannel has a dimension between about 0.1 μm andabout 500 μm.
 30. The microfluidic device of claim 1, further comprisingone or more of: a sampling system for introducing the at least firstfluidic material into the first microchannel; a detection system fordetecting one or more analytes in the first microchannel; a data storagesystem; a fluid control system for controlling fluid transport anddirection in the first microchannel; a temperature detector fordetecting the temperature of a portion of the body structure; and, acurrent detector for detecting current in the first microchannel. 31.The microfluidic device of claim 1, further comprising a fluid directionsystem, which fluid direction system electroosmotically transports thefirst fluidic material through the at least first microchannel at amobility of at least about 1×10⁻⁵ cm²V⁻¹s⁻¹.
 32. The microfluidic deviceof claim 31, wherein the fluid direction system comprises one or moreof: an electrokinetic controller and one or more electrodes.
 33. Amethod of fabricating a microfluidic device, the method comprising:fabricating a polymeric material to form a substrate having at least onesurface, which surface has at least a first channel disposed therein,which first channel has a zeta potential associated therewith, whichzeta potential supports an electroosmotic mobility of at least about1×10⁻⁵ cm²V⁻¹s⁻¹ for at least a first fluidic material, said firstfluidic material comprising from about 1 mM to about 100 mM sodiumborate buffer at a pH of from about 6 to about 9, said first channelhaving a dimension in a range from about 0.1 μm to about 500 μm; and,overlaying a cover layer on said at least one surface, said cover layerenclosing said first channel, and wherein said substrate and said coverlayer together comprise one or more port disposed therein, which one ormore port is in fluid communication with said first channel.
 34. Themethod of claim 33, wherein said polymeric material is selected from:polydimethylsiloxane (PDMS), polyurethane, polyvinylchloride (PVC),polystyrene, polysulfone, polycarbonate, polymethylmethacrylate (PMMA),and polytetrafluoroethylene.
 35. The method of claim 33, saidfabricating comprising molding said polymeric material to form saidsubstrate.
 36. The method of claim 33, said fabricating comprisinginjection molding said polymeric material to form said substrate. 37.The method of claim 33, said fabricating comprising embossing said atleast one surface of said substrate to form said at least one channel.38. The method of claim 33, further comprising treating said firstchannel to provide the zeta potential.
 39. The method of claim 38,wherein said treating comprises treating said first channel with afluorinated modifier compound.
 40. The method of claim 33, wherein saidpolymeric material comprises PDMS and said treating comprises exposingsaid first channel to oxygen plasma.
 41. The method of claim 33, whereinsaid overlaying comprises bonding said cover layer to said surface ofsaid substrate.
 42. A method of flowing a fluidic material through amicrochannel in a polymeric substrate, which microchannel has a zetapotential associated therewith, the method comprising: applying avoltage to the fluidic material in the microchannel in the polymericsubstrate, thereby flowing the fluidic material through the microchannelat a mobility of at least about 1×10⁻⁵ cm²V⁻¹s⁻¹.
 43. The method ofclaim 42, wherein the fluidic material comprises a sodium borate bufferhaving an ionic strength between about 1 and about 100 mM and a pH fromabout 6 to about
 9. 44. The method of claim 42, wherein the fluidicmaterial has an ionic strength between about 1 and about 10 mM and a pHfrom about 7 to about
 9. 45. The method of claim 42, wherein applyingthe voltage to the fluidic material in the microchannel comprises usinga voltage controller, which voltage controller is in electrical contactwith the fluidic material.
 46. The method of claim 45, wherein thevoltage controller is in electrical contact with the fluidic material inat least one well, which well is fluidly connected to the at least onemicrochannel and comprises an electrode disposed within the well. 47.The method of claim 42, further comprising detecting the fluidicmaterial in the microchannel.
 48. The method of claim 42, comprisingdetecting the fluidic material using a detector mounted proximal to themicrochannel.
 49. The method of claim 42, wherein the polymericsubstrate is fabricated by bonding a first polymeric surface to a secondpolymeric surface, wherein the microchannel is formed between the firstpolymeric surface and the second polymeric surface.
 50. The method ofclaim 42, wherein the polymeric substrate is fabricated from:polydimethylsiloxane (PDMS), polyurethane, polyvinylchloride (PVC),polystyrene, polysulfone, polycarbonate, polymethylmethacrylate (PMMA),or polytetrafluoroethylene.
 51. The method of claim 42, wherein thepolymeric substrate comprises at least about 50% polymeric materials.52. The method of claim 42, wherein the at least one microchannel isembossed as at least one groove in a substantially planar portion of thepolymeric substrate and wherein a cover layer overlays the at least onegroove, thereby forming a closed microchannel.
 53. The method of claim42, comprising flowing the fluidic material through the microchannel atan electroosmotic mobility of at least about 5×10⁻⁵ cm²V⁻¹s⁻¹.
 54. Themethod of claim 42, comprising flowing the fluidic material through themicrochannel at an electroosmotic mobility of at least about 1×10⁻⁴cm²V⁻¹s⁻¹.
 55. The method of claim 42, wherein the microchannelcomprises a surface coating.
 56. The method of claim 42, wherein themicrochannel comprises a surface coating, which coating is provided tothe first microchannel by a process selected from: exposure to afluorinated modifier compound, exposure to a detergent, exposure to amaterial having charged functional groups associated therewith, andexposure to a fluorocarbon.
 57. The method of claim 42, furthercomprising flowing the fluidic material through a second microchannel atan electroosmotic mobility of at least about 1×10⁻⁵ cm²V⁻¹s⁻¹.